When speech or sound signals are transmitted by a packet communication system typified by internet communication, a mobile communication system and so forth, compression and coding techniques are commonly used in order to improve the efficiency of transmission of speech or sound signals. In addition, in recent years, there is an increasing need for not only a technique to simply encode speech or sound signals at a low bit rate but also a technique to encode wider band speech or sound signals.
To meet this need, various techniques for encoding wideband speech or sound signals without significantly increasing the amount of information after coding have been developed. For example, according to Patent Document 1, spectral data is obtained by converting acoustic signals inputted in a certain period of time and the characteristic of a high frequency band of this spectral data is generated as auxiliary information and outputted with encoded information of a low frequency band. To be more specific, spectral data of a high frequency band is divided into a plurality of groups, and information to specify the low frequency band spectrum most similar to the spectrum of each group is provided as auxiliary information. In addition, according to Patent Document 2, discloses a technique for dividing a high frequency band signal into a plurality of subbands, determining the degree of similarity between a signal in each subband and a low frequency band signal and modifying, depending on the determination result, the content of information (the amplitude parameter in each subband, the position parameter of the similar low frequency band signal and the signal parameter of the difference between the high frequency band and the low frequency band.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-140692    Patent Document 2: Japanese Patent Application Laid-Open No. 2004-4530